Catheters with distally mounted balloons are well known for their usefulness in medical applications and in particular interventional procedures, for opening blood vessels or other passageways in the body that may be blocked by obstructions or stenosis. Dilatation catheters are generally formed from thin, flexible tubing having an inflatable balloon at or near a distal tip of the tubing that can be inflated with fluid pressure communicated to the balloon through a lumen of the tubing. In a typical angioplasty procedure, the balloon dilatation catheter is passed through the vasculature to the location of a stenosis in an artery, and the balloon is inflated to a predetermined size and shape to open the blocked artery. Balloon catheters are not limited in their use to the relief of arterial stenosis but have been found useful in many medical applications involving not only insertion into blood vessels but also involving insertion into a variety of body cavities.
It is desirable for balloons of balloon catheters to be capable of inflating to a diameter of typically five to six times their uninflated diameter in order to be able to open an obstructed vessel or deploy a stent prosthesis within a vessel. Other desirable properties of balloons for such interventional procedures include superior strength, softness, flexibility together with a thin, low profile which are important for achieving the performance characteristics necessary to fold the balloon in an uninflated state. This uninflated configuration is important for achieving acceptable tracking and crossing or recrossing the area of the obstruction or stenosis in a vessel. In addition, properties of burst strength, compliance, and fatigue have been increasingly important in the continuing effort to create thinner, lower profile balloons for interventional procedures with the ability to track and cross or recross increasingly obstructions in relatively narrow passages of distal vessels. For purposes of this description, the ability to cross is defined as the ability of a balloon of a balloon dilatation catheter to pass through a stenosis; the ability to recross is defined as the ability of the balloon of a balloon dilatation catheter to pass through a stenosis more than once, or to pass through more than one stenosis; and the ability to track is defined as the ability of the balloon of a balloon dilatation catheter to pass over a guidewire through the tortuous curves of the vasculature, in being guided to and from the location of a stenosis.
Polymeric materials that have been used for making medical devices, catheters, dilatation catheters, and balloons for balloon dilatation catheters include polyethylene, polyolefins, polyvinyl chloride, polyester, polyimide, polyethylene terephthalate (PET), polyamides, nylon, and the like. Also included among the known materials disclosed in patents are ethylene-butylene-styrene block copolymers admixed with low molecular weight polystyrene and, optionally, polypropylene, and similar compositions employing butadiene or isoprene in place of the ethylene and butylene; copolyesters; thermoplastic rubbers; siliconepolycarbonate copolymers; and ethylene-vinyl acetate copolymers. Balloons made of soft polyolefin or ethylene copolymers materials are typically foldable, and track and cross well, so that they can often be used more than once, and can be used to cross multiple lesions. However, such balloons also commonly have high balloon compliance and low burst strengths, with ratings of rated burst pressure of about 8-9 atm, and a mean burst pressure of about 10-15 atm. Balloons made from polyethylene terephthalate (PET) are commonly stronger, with a higher rated burst pressure of about 14-18 atm, and a mean burst pressure of about 18-25 atm. However, dilatation catheter balloons made of PET are generally stiff, not readily foldable, and are susceptible to acquiring defects from mechanical handling. Dilatation catheter balloons made of PET are also susceptible to pin-hole failures that can cause jet-streaming of pressurized fluid within an artery, and can lead to a dissection of the artery. As a result, to reduce the likelihood of pin-hole failures, clinical applications of balloons made of this type of material have generally been limited to thicker balloons that are commonly limited to a single use, and for crossing a single lesion.
Examples of prior art compositions that may be suitable in forming medical devices such as catheters, dilatation catheters, and balloon materials for use in angioplasty procedures include U.S. Pat. No. 4,753,980 (Deyrup); U.S. Pat. No. 4,172,859 (Epstein); U.S. Pat. No. 4,490,421 (Levy); U.S. Pat. No. 5,091,478 (Saltman); U.S. Pat. No. 5,306,246 (Sahatjian et al.); U.S. Pat. No. 4,254,774 (Boretos); U.S. Pat. No. 4,964,409 (Tremulis); U.S. Pat. No. 5,017,325 (Jackowski et al.); U.S. Pat. Nos. 4,093,484 (Harrison et.al.); U.S. Pat. No. 4,154,244 (Becker et. al.); and U.S. Pat. No. 4,254,774 (Boretos), all of which are incorporated herein by reference. These references are presented by way of example only and are not intended to be exhaustive of the prior art.
It would be desirable to provide a urethane polymeric blend for balloons for balloon dilatation catheters with a combination of the best features of the softer balloon materials and the stronger balloon materials, including good flexibility, folding, track, cross and recross, with a thin, low profile, high resistance to fatigue, low compliance, and high burst strength, with a lower susceptibility to defects through mechanical handling, and a lower susceptibility to pin-hole defects, compared with balloons made from PET. The present invention meets these needs.
Another object is to provide such balloons which, because of their flexibility and thin walls, are more readily collapsible and more easily transportable in the body.
It is also an object of the invention to provide such balloons which exhibit very little elongation or creep radially, collectively referred to herein as radial expansion, when inflated to the pressure necessary to perform the desired medical procedure.
A further object is to provide such balloons which, because of their superior physical properties, can be used in medical procedures with a greater probability of success.
Another object is to provide such balloons which, because of their superior physical properties, can be used in medical procedures such as a stent deployment balloon.
Still another object is to provide a process for fabricating such balloons.
These and other objects will become apparent from the following discussion of the invention.